With rapid popularization of intelligent terminals and mobile applications in recent years, a mobile communications network has also gained rapid development. Meanwhile, data communication load that a cellular access network needs to bear also becomes increasingly heavy. However, advance of technologies helps a wireless local area network (WLAN) achieve an increasingly high data throughput. In addition, compared with a cellular access network, the WLAN has low network deployment costs and OPEX and supported by a large number of terminals. Therefore, a part of data transmitted by using the cellular access network by user equipment (UE) may be offloaded to the WLAN for transmission, thereby reducing load of data transmission in an existing mobile communications network.
In the prior art, an access network discovery and selection function (ANDSF) entity is disposed in a core network, and the ANDSF entity sends an inter-system routing policy (ISRP) to a UE by using a user plane. The ISRP includes at least one type of a flow based (Flow based) routing policy, and each flow based routing policy includes at least one routing rule. Therefore, the UE may determine, according to a description and a rule priority of a to-be-sent traffic flow, a flow based routing policy that matches the traffic flow; determine, according to an access network priority, a routing rule in the flow based routing policy that matches the traffic flow; then, the UE sends out the traffic flow by using an access network specified in the routing rule, where the access network is a cellular access network or a WLAN. In this way, the UE can transmit data by using the cellular access network and the WLAN.
However, an ISRP is application layer information, and the UE needs to send an ISRP received from an application layer to a communications module at a bottom layer of the UE for processing; there is an extra matching operation at the bottom layer of the UE in addition to existing flow matching executed by using a filter for a cellular access network transmission bearer, which causes complex implementation of a process in which the UE selects a WLAN route for a traffic flow. In addition, because update of the ISRP as an application layer approach is slow, it is difficult to consider dynamic information of the cellular access network and the WLAN network during generation of the ISRP, which results in low efficiency when the UE selects, according to the ISRP, the WLAN to transmit data.